Segmental grinding wheel



Sept. 15, 1936. T. LARSSON 4 SEGMENTAL GRINDING WHEEL Filed Nov. 9, 1955 Patented Sept. 15, 1936 UNITED STATES SEGMENTAL GRINDING WHEEL Thure Larsson, Worcester, Mass, assignorto Norton Company, Worcester, Mass., a corporation of'Massachusetts Application November 9, 1935, Serial No. 49,062

10 Claims. (Cl. 51-207) This invention relates to segmental grinding wheels and more particularly to wheels composed of bonded abrasive segments which are especially adapted for grinding wood pulp, metals and other materials. lhe standard segmental wheel is made up of a number of abrasive segments or sectors which are arranged to provide a substantially continuous grinding surface. These segments are usually composed of silicon carbide or crystalline alumina abrasives bonded. together in arequired shape by means of vitrified ceramic materials which have been developed by firing under suitable temperature conditions as a .porcelanic or glassy bond.

is These abrasive segments may be held in place by clamping devices which engage shoulders there on and secure them to a central support, or they may be cemented together by a suitable material, suchas a resinoid, and held rigidly in position 20 by means of large clamping plates engaging the two ends of the wheel. The pulp stonesare usually madeof several annular courses of segments, so as to provide a wheel of the desired length. A segmental wheel for grinding knives 25 or for snagging-metal castings may be made of a single course of segments arranged as an annulus, which are held together by a suitable cement and'mounted on clamping plates engaging beveledshoulders on the opposite sides of the 30 wheel.

These grinding wheels are often subjected to large temperature changes when put into use, due to the frictional heat generated at the'grinding surface. A wheel employed in snagging a metal 5 castingis used without cooling water; while a pulp stone may be subjected first to the cold temperature of a northern winter and then run inhot water at a temperature of 160 F. or higher. Moreover if such a pulpstone should be operated accidentally without the usual flow of water, the generated heat/caused by pressing the logs of wood hydraulically against the wheel periphery may be abnormally high for a short period of time.

It is customary to fill the crevices between the 1,815,108 dated July 21, 1931, this Babbitt metal has been shaped as spaced posts which are adapted to be deformed, if the lateral pressure of the segments due to overheating the wheel becomes too great, and thus permit th e necessary ex- 5 pansion of the wheel. The present invention relates to an improvement over that construction as well as over the various other types of segmental wheel herein described.

. When the periphery of the grinding wheel is 10 subjected to frictional heat, the wheel expands first at the periphery and then gradually inwardly. If the filling material in the crevices between the segments is riot easlly'deformed under the pressureof the expanding abrasive bodies, its resistance to compression is likely to cause breakage of the wheel." It is desirable that the .flller be deformable under all of the-conditions of using the wheel and that it. deform to such an-extent, as the abrasive segments become heated, that the segments may expand into the crevice space formerly occupied by the filling material.

The primary object of this invention is to provide a segmental grinding wheel which may be subjected to the normal or abnormal heating conditions incident to a grinding operation without danger of wheel breakage.

Another object is to provide a filling material for the crevices between the abrasive seg nents which is capable of deforming as the abrasive segments expand under a rise in temperature and to such an extent as not to impose an abnormally high back. pressure against the segments and endanger the same. parent in the following disclosure.

In accordance with this invention, the desirable properties of hard rubber are employed without detrimental results in amaterial used for filling the crevices between the abrasive segments and holding the comers thereof, protected against breakage while permitting expansion of the wheel as the temperature rises. One manner of accomplishing this is to make the hardrubber filler as a' cellular body which has spaces within which 4.5

the structure may deform and permit the adjacent wheel faces to approach one another. Thespaces within the. cellular rubber may be filled with a material, such as large granules of cork, which in. itself provides cellular spaces ca- 50.

pable of permitting such deformation. Abrasive material may also be incorporated in the rubber to give desirable properties thereto. This invention, moreover, contemplates the provision of a special type of rubber which has the ability to Further objects will be ap- 35 when reheated, will close the spaces left by the permanent deformation of the rubber.

In order that the invention may be more fully understood, reference is tobe-"had to the accompanying drawing, in which:

Fig. 1 is a fragmentary sectional View of one type of pulp stone embodying this invention;

Fig. 2 is a vertical elevation of the wheel shown in Fig. 1';

Fig. 3 is a sectional view of a cemented wheel; and v Figs. 4 and 5 show in fragmentary enlarged sections the structural arrangement of two types of crevice filler employed. v

Figs. 1 and 2 illustrate a Norton type of pulp stone embodying this invention, in which the rotatable support may be a hollow metal drum or. a concrete body, as disclosed in the above men- 1 tioned Patent-No. 1,815,108and the patent to to the drum in desiredpositions by means of the wedge blocks i l seated against beveled shoulders on the dove tailed portions of the segments and secured to the drum by means of the elastic metal segments.

bolts l6, as described in the U; S. patent to, Larsson and Beth 1,736,161 of November 19,1929.

The bolts are adjustably threaded into the wedge blocks and are secured by means of nuts ll engaging the inner face of the drum. Babbitt metal or other suitable seats 20 may be provided on the .beveled shoulders of the segments for engagement with the wedge blocks. The crevices are filled with a rubber compound, as hereinafter described, which surrounds the outer faces of the wedge block [4. and extends outwardly to the wheel periphery. This compound may also be placedin the lower spaces between the bolts l6 and the These crevices are ordinarily very narrow, but they have been shown exaggerated in size for the purpose of emphasizing an im-- portant feature of the construction.

Similarly, a grinding wheel of the type shown in the patent to Larsson 1,979,074 of October 30, 1934 comprises a plurality of segments cemented together and arranged to, be supported on carrying plates. If such a wheelis made up of multiple courses of segments, the latter may be shaped and arranged as illustrated, in Fig. 3 wherein they are cemented together to provide a substantially integral or unitary structure. In this wheel, the segments 30 are cemented to each other-by a suitable cement, such as herein de-; scribed, and which may be used, if desired, in conjunction with a'resinoid or a rubber compound to form an integral wheel structure. The outer side faces. of. the two .rows of segments are so to hold the stone together during rotation thereof. As an aid to strengthen the wheel against disruptive forces, a'metal ring 36 may be bemented in grooves formed in the inner adjacent faces of the two courses of segments. This metal ring may be made of suitable material, such as one which has substantially the same coefficient of expansion as has the ceramic bonded abrasive. For use with a ceramic bonded silicon carbide segment, a steel having about 30% of nickel may be. used. This ring maybe cemented in the groove by any of the compositions hereinafter described or by a special cement comprising rubber, sulfur and silicon carbide powder in suitable proportions, such as 1 part of a hard vulcanized rubber compoundcontaining 20 to 25% of sulfur combined with 5 to 10 parts of the abrasive. Also, various resinolds, such as a bakelite phenolic condensation product, may be used as the cement forholding the ring in place and, if desired, for cementing the inner portions of the abrasive segments together, provided a deformable filler as herein described is located inthe outer portions 38 ofthe-crevices where the; heat stresses are high. The resinoid may contain, 'various inert fillers which aid in compensating for differences in expansion, as is well known,..-,

Various other types of segmental grinding "wheels or stones may be madeas-regards the nature of the bond and abrasive used and the shapes and purposes of the wheel; but in every case the segments will beso arranged as to pro vide spaces therebetween, which are to be filled. with a suitable material. The figures of the drawing above described are thereforeintended to be merely illustrative of the general principles of the invention and not as limitations as to thetype of structure to which this invention applies. In these various typesof grinding wheel, the

crevices 2t and 38, which run both circumferen v tially and laterally of the wheel, are filled to, a

required extent with a rubber composition as herein described,

If solid hard vulcanized rubber were used .to fill completely the crevices between the abrasive segments, the resistant force ofieredby thev hard not deform materially with the increase in temperature, and it is not sufficiently;resilient or. elastic to permit the required expansion'of the segments. Consequently this substantially rigid material resists expansion of the segments to the point that breakage occurs. either across thecorners of the segments or through their narrow dove-tailed portions.

In accordance with the primary feature; of this invention, I provide the hard rubber with.

cellular spaces within which the ,hard rubber may deform under the pressure of. the expand The cellular spaces are ing abrasive segments. of such sizes and total volume that the rubber is made up largely of posts and webs which are sufiiciently attenuated so that they. willbuckle orotherwise deform when subjected to excessivepressure. Although the cellular rubber may :be

madeby the standardprocedure of making'sponge I 570 (iii ber material. 'The sulfur is preferably mixed into the rubber in a suitable amount for vulcanization to ahard rubber. Hence, as shown in Fig. 4, the crevices 24, or any other portion of the wheel, may contain a compound of rubber to intermixed with large cork granules 42, which have been compounded as herein described. As shown in Fig. 5, this composition may also include abrasive grains 44 of suitable size, kind and quantity to give desired properties to the bompound. Either the cork or the abrasive or both may however be omitted, provided the hard vulcanized sponge rubber is employed.

As a further feature of this invention, I propose to use a rubber compound which differs materially from the standard hard vulcanized rubber in that this compound will soften as the temperature rises and thus interpose a continually decreasing resistant force to the'expansive action within the wheel. To this end, I compound the hard rubber with a modifying agent, such as mineral rubber, which permits that softening or deformation with the increase in temperature. Mineral rubber is an asphaltite, such as gilsonite and grahamite, which has the capacity of mixing with. rubber and changing its plwsical characteristics as here required. The proportions of rubber and mineral rubber as well as the amounts of sulfur used in the vulcanization process may be varied widely.

The abrasive material is used to give the crevice filler a desirable abrasive quality as well as to decrease the deiormabiiity of the rubber compound to a satisfactory extent, whereby the corners oi the abrasive segments may be adedown rapidly and leave the crevices unfilled and the corners of the segment exposed.

These various ingredients may be communded in widely varying proportions, depending upon the sizes and volume of the cellular spaces desired and the degree of deformability which is best suited for a given use of the wheel. For example, the rubber compound may be made of the following compositions in percentages by weight:

Per cent liubben db 5b oi as 27 27 in it Mineral rubber 2i l2 Fs'ilicon carbide 23 23 2b 23 Rubber compound 1@ lbb lob ldb Corie lid 25 The silicon carbide grains in the above compositions are of to mesh, or oi such a size as will just pass through a screen of do meshes per linear or other similar material is not satisfactory because or the absence or these spaces ior receiving the proportions of these ingredients.

ing the deforming material. It is to be noted that the rubber, sulfur and abrasive composition of the first column in the table would not be satisi'actory unless made with pore spaces, which may make uptwenty-five to forty per cent of the total rubber content, for example, just as does the cork in the other examples noted. It will also be appreciated that the amount of the mineral rubber may be varied widely depending upon the conditions of use of the grinding wheel.

One mayemploy the various types of rubber used in the industry, and many other modifying agents may be used in place of the mineral rubber for softening the hard rubber compound. For example, cumar or paracumarone or such waxes as beeswax or Montan wax are suitable. One may use coal tar pitch or petrolatum for the same purpose. Likewise brown or white factice is usable. The brown factice is a reaction prodnot of vegetable oils and sulfur, while the white factice is a reaction product of sulfur chloride and vegetable oils. It is evident that one may compound these with the rubber in desired proportions depending upon the deformability desired. The larger the amount of the mineral rubber or other softening agent, the greater will be the deiormability of the rubber compound in the grinding wheel. Hence the characteristics of the wheel may be varied materially by chang- It will also be understood that one may use the standard fillers within the rubber, such as alumina, clay, iron oride, etc., in place of or supplementing the abrasive filler above specified. These may be used in various proportions depending upon the characteristics desired in the rubber, as is well understood in the industry.

In order to make wheels of the types shown in the drawing, the segments may be assembled in position with sheets of the rubber compound interposed therebetween. The rubber compound will have been previously made in accordance with the standard practice, such as by adding the sulfur, cork and abrasive to a sheet of crude rubber while repeatedly passing it through calendaring rolls, or by mixing them in a rubber kneading machine, after which a sheet of the re quired thickness is rolled out and cut to size. If an iron center or a concrete support is to be used in the structure of Fig. l, the iron center, wedge blocks, etc. or the concrete reinforcements may be put in place at this time. Thereafter adjustable iron bands are placed around the segments and the adjustments tightened in order to force the segments into full contact with the rubber compound in the crevices therebetween. These bands are lelt bu place while the assembled ring of segments is heated in a vulcanizing oven at the required temperature to vulcanize the rubber compound and make a hard rubber thereof. it is ordinarily desired that the sulfur content be sufilcient to produce hard rubber. A soft rubber would be too compressible and elastic and would not have the desired properties. After the rub ber compound has been vulcanized, then the elastic bolts of Fig. 1 maybe tightened to secure the segments on the drlun. 0r, a concrete center may be cast in place within the abrasive annulus and other operations performed as is desired to form a concrete wheel. shown in Fig. 2 is to be made, then of course the iron rings will have been put in place initially together with a suitable compound to cement them in place.

If a wheel of the type It is to be understood that the deformable rubber compound need not expand back to its original size or thickness when the stone has cooled and the pressure due to heat expansion has been released. When the stone cools down and the rubber remains deformed, there may be Having thus described this invention, what I claim as new and desire to secure by Letters Patent is:

1. An abrasive article comprising a plurality of segments of bonded abrasive material cemented together and containing a cellular vulcanized hard rubber compound in the spaces therebetween.

2. A grinding wheel comprising a plurality of abrasive segments spaced and arranged to form an abrasive surface, means to secure them rigidly in position in a spaced relationship, and a filler in the crevices between the abrasive segments comprising a vulcanized rubber compound having a cellular structure which contains spaces into which the rubber material may be deformed as the abrasive segments expand due to a temperature rise in the wheel.

3. A grinding wheel comprising a plurality of abrasive segments spaced and arranged to form an abrasive surface, means to secure them rigidly in position in a spaced relationship, and a filler in the crevices between the abrasive segments comprising a vulcanized rubber compound containing rubber and sulfur proportioned to form hard rubber intermixed with cork granules which are present in sumcient amount and are of such size as to permit deformation of the rubber as the wheel segments expand.

4. A grinding wheel of the type covered by claim 2 in which the rubber compound comprises a rubber sulfur compound proportioned to form hard rubber and intermixed with a modifying agent capable of causing the filler to soften as the abrasive segments expand and temperature rises within the wheel.

therefore be reinforced and strengthened by the filler adjacent thereto.

5. A grinding wheel comprising a plurality of 2 in which abrasive material is incorporated in the rubber compound.

7. A grinding wheel comprising a plurality of abrasive segments shaped and arranged to form an abrasive annulus, means to secure the abrasive segments substantially rigidly in position for a grinding operation and a filler in the crevices between the segments comprising a cellular vulcanized hard rubber compound containing abrasive material intermixed therein and a modifying agent which causes the rubber to soften and deform under the increasing pressure of the heat expanding segments during a grinding operation.

8. A grinding wheel of the type covered by claim =7 in which the rubber compound comprises large cork granules which are present in such an amount and are of such size as to permit expansion of the abrasive segments and deformation of the rubber compound during use of the wheel.

9. A segmental grinding wheel comprising bonded abrasive segments and a vulcanized rubber filler therebetween containing rubber and sulfur proportioned to form hard rubber, abrasive grains, and cork granules as large as 20 grit size which are present in sufficient amount to permit deformation of the compound under pressure.

10. A segmental grinding wheel comprising bonded abrasive segments secured together and a vulcanized rubber filler therebetween containing rubber and sulfur proportioned to form hard rubber, abrasive grains, large cork granules providing space for deformation of the rubber and a modifying agent capable of permitting the rubber compound to soften as the temperature rises.

THURE LARSSON. 

